Conventional heavy metal separation processes involve the utilization of ion exchange (see Sengupta, A. K. (Ed.), Ion Exchange Technology, Technomic Publication Co. Inc., Pensylvania, 1997), precipitations, or membranes. Applicable membrane technologies include nanofiltration, ultrafiltration, and reverse osmosis. Microfiltration membranes containing metal chelating groups have also been used for heavy metal adsorption and separation (see Konishi et. al., Binary Metal Ion Sorption During Permeation Through Chelating Porous Membranes, J. Memr. Sci., 111:1, 1996). Various adsorbents and ion exchange materials have been reported for metal ion entrapment. Conventional ion exchange groups are amines, sulfonic and carboxylic group such as amidoxime and phosphoric acid (see Jyo, A. et. al., Preparation of Phosphoric Acid Resins with Large Cation Exchange Capacities from Macrorecticular Polyglycidyl Methacrylate-Co-Divinyl-Benzene Beads and Their Behavior in Uptake of Metal Ions, J. Appl. Polym. Sco., 63:1327, 1997). Acrylic acid (see Ibrakin, N., et al., Novel Cation Exchange Composites Resulting from Polymerization/Cross-linking of Acrylic acid/N-Methylolacrylamide Mixtures with Cellulose, J. Appl. Polym. Sci., 49:291, 1993), aminomethyl-phosphoric acid (AMP) (see Maeda, H. et al., Studies of Selective Adsorption Resin XXX, Prep. of Macrorecticular Chelating Resins Containing Aminomethylphosphoric Acid Groups From Methylmethacrylate/Divinylbenzene Copolymer Beads and their Adsorption Capacity, J. Appl. Polym. Sci., 33:1275, 1987) etc. have been reported in the literature. The reported order of the chelate stability with the AMP resins was Cu+2>Pb2+>Ni+2>Ca+2. Traditional ion exchange resins have been used extensively to recover heavy metals and to simultaneously obtain high quality water for reuse.
Porous membranes containing chelating agents provide enhanced mass transfer due to convection (see Konishi et. al., Binary Metal Ion Sorption During Permeation Through Chelating Porous Membranes, J. Memr. Sci., 111:1, 1996). Functionalized membranes containing a large number of polymer chains for binding multiple metals to increase the capture capacity of the membranes have been reported (see Bhattacharyya et al., Novel Poly-L-Glutamic Acid Fictionalized Microfiltration Membranes for Sorption of Heavy Metals at High Capacity, J. Membrane Sciences, 141, 1998, 121-135). Cellulose and its derivatives provide the most versatile and inexpensive starting materials. Pb++ ion with a hydration radius of 0.4 nm would require a maximum surface entrapment capacity of 34 mg Pb/g membrane with a representative 50 m2/g BET membrane surface area for even only single- site available for one Pb++ ion interaction. Obviously, the metal absorption capacity is still quite low for an industrial application.
To remove toxic heavy metal ions from water supply systems for drinking, city water supply, recreational or other industrial use, or reuse has been an important issue for everyone. Safety and health concerns are always a vital issue in the modern living. An easy, effective, and reliable method of removing toxic heavy metals from the water systems, and dissolving the scales of calcium or magnesium can be accomplished by using γ-polyglutamic acid (γ-PGA, H form) and/or one or more γ-polyglutamates (in Na+, K+, and/or NH4+ forms) and/or one or more γ-polyglutamate hydrogels (prepared from γ-polyglutamates in Na+, K+, and/or NH4+ forms). Moreover, the aggregates formed from the heavy metals and γ-polyglutamates can be easily separated by press filtration, or membrane ultrafiltration or by other centrifugation devices.